Laminated cookware

ABSTRACT

A multiple ply laminated cookware container includes a core ply of high strength and relatively low thermal conductivity, such as carbon steel, which is sandwiched between non-ferrous plies, such as aluminum. A frit anchor ply may be bonded upon the aluminum ply nearest the interior of the container and a non-stick coating, such as Teflon may be bonded to the frit ply. Preferably, a decorative coating, such as a porcelain enamel, is bonded to the aluminum ply nearest the exterior of the container. The thickness of the steel and non-ferrous plies may be varied so as to suit structural as well as thermal qualities of given areas of the container.

United States Patent 1191 Racz 1451 Jan. 29, 1974 LAMINATED COOKWARE['76] Inventor: Nick S. Racz, 4800 Chicago Beach Dr., Chicago, 111.60645 [22] Filed: Jan. 15,1970

[21] Appl. No.: 3,044

158] Field of Search 220/64, 63; 117/97, 75, 71,

1/1961 Scavullo 126/390 8/1967 Holcomb 117/70 C X PrimaryExaminer-George E. Lowrance Assistant Examiner-Stephen Marcus Attorney,Agent, or Firm-Molinare, Allegretti, Newitt & Witcoff 57 ABSTRACT Amultiple ply laminated cookware container includes a core ply of highstrength and relatively low thermal conductivity, such as carbon steel,which is sandwiched between non-ferrous plies, such as aluminum.

[56] References Cited A frit anchor ply may be bonded upon the aluminumUNI ED S AT PATENTS ply nearest the interior of the container and a non-3,241,545 3/1966 Reinert et a] 220/64 x Suck coatmg such as Teflon maybonded to the 2,057,254 10/1936 Sommer 220/64 Preferably a decoratwecoatmg' Such as a Force 2,511,404 6/1950 Glenkey 6181.." 220 64 x lainenamel, is bonded to the aluminum P y nearest 2,975,072 3/1961 Bryant eta1. 117/97 x the exterior of th ntain r. Th thickn ss of the 3,393,0867/ 1968 Keating 220/64 X steel and non-ferrous plies may be varied so asto suit 2,841,137 7/1958 Chace 220/63 X structural as well as thermalqualities of given areas of 3,511,690 5/1970 Aharoni 220/64 x thecontain 3,419,414 12/1968 Marks 117/75 X 9 3,143,241 8/1964 Howell220/64 17 Claims, 2 Drawing Figures 26 l: l 1 11 1! i 1 I 1 I 1 1? 5 UN,1 1 I /4 \j: I? E I 6 i Q A;

S e24 a. 1; 20 i 1 'i- I I "A "7 h 4 22 n7 P 2: Q i i 1 1 1 l l l I;

1 LAMINATED COOKWARE This invention relates to cookware and, moreparticularly, to laminated cookware containers,

Ideally, cookware containers should satisfy at least the followingcriteria: (I) the mechanical strength of the cookware must be sufficientto provide adequate support for the container and its contents, (2) thecontainer surfaces must be non-toxic to permit the preparation ofhealthy non-contaminated dishes, (3) the con tainer should resist bothrust or oxidation and washing solutions, (4) that portion of thecontainer which is in contact with the source of heat for cooking shouldhave a relatively high thermal conductivity to enhance heat transfer tothe food being cooked so as to enable fast, economical and uniformheating of the food without degrading the non-stick finish and othercoatings of the container, (5) that portion of the container not incontact with the source of heat for cooking should have a relatively lowthermal conductivity to reduce heat losses from the food thus enablingfast and economical heating of the food, (6) the container should beeasy to clean'after use, (7) the container should resist wear well, (8)the container should have a pleasing aesthetic appearance, (9) the.costs of the container should be low. I

In view of some ofthese considerations, both aluminum and stainlesssteel cookware containers have come into widespread use.Aluminumcontainers have come to be preferred over those of stainlesssteel primarily because containers can be made of aluminum which satisfya greater number of the above criteria for cook'- ware 'containers't-hanstainless steel containers at a cost less than that of'the stainlesssteel.

An analysis of an aluminum cookware container based on the above list ofcookware criteria will point out the relative advantages anddisadvantages of this material. Aluminum if thick enough has sufficientmechanical strength for this purpose. It is non-toxic and provides somedegree of resistance to oxidation and washing solutions lt has excellentthermal conductivity, thereby enhancing heat flow from the source to thefood, but it does not retard heat losses through those parts of thecontainer which are not in contact with the heat source. It is notparticularly easy to clean, and has a tendency to stain or discolor innormal use. It is fairly wear resistant. It can be made fairly pleasingin appearance initially, but the tendency to stain mentioned above, andthe tendency of the surface to dull with time and use make it lessdesirable than stainless steel, glass or other ceramics from thisstandpoint. The costs of aluminum containers are greater than, say,carbon steel but less than stainless steel.

A similar comparison for a stainless steel container shows its relativeadvantages and disadvantages. It has considerably greater mechanicalstrength than aluminum. It is non-toxic. It resists both oxidation andwashing solutions. Its thermal conductivity is much poorer than that ofaluminum, thus it does not provide as good heat tlow from the heatsource to the food as aluminum, but it does somewhat retard heat lossesthrough those parts of the container not in contact with the source. Itis somewhat easier to clean than aluminum, but the removal of baked onfood may still be quite difficult. Its resistance towear is very good.It can be made with a bright finish which is pleasing in appearance, andwill not dull or stain appreciably with age or use. Finally, the costsof stainless steel containers are, as noted above, higher even thanthose of aluminum.

Because of some, though not necessarily all, of the short-comings of thevarious materials used in cookware container manufacture, themanufacturers of these containers haveresorted to several means toimprove their products and more closely match the ideal containercriteria. Since the major disadvantage of mild steel as a material forcookware containers is its tendency to rust, those manufacturers who useit have completely covered the container with some material which iswear resistant, and protects the steel from contact with oxygen, such asvarious enamels, etc. However, there is as yet no such covering that cannot be chipped or cut through, thus exposing the mild steel beneath andpermitting rust to begin.

Manufacturers who use aluminum frequently coat the exterior of theircontainers with a finish which is decorative, stain resistant, andeasier to clean than the aluminum, thus improving the quality of theirware with respect to two of the criteria listed in a single operation.They also may coat the interior of the container with a non-stickfinish, such as a member of the polytetraflouroethylene (P.T.F.E.)family, which makes the container much easier to clean, and, since thesecoatings are available in different colors, may also enhance theapearance of the container. Since it can be supplied with a lastingattractive looking finish, stainless steel does not need to be given adecorative exterior coat. The ease of cleaning stainless steelcontainers would, however, be greatly improved if they could be coatedon the interior with a non-stick finish, but stainless steel is notnearly as good a substrate for these types of finishes as is aluminum.

Thus, it is seen that of these three major cookware container materials,steel, aluminum, and stainless steel, aluminum is the most amenable toimprovement by the application of different types of finishes. However,this improvement is not without its price. One serious disadvantageoccurs when the decorative finish applied to the exterior of thecontainer is a porcelain enamel. In order to provide an adequate finishwith this type of enamel, the coated container must be heated'to atemperature in excess of 1000F. Commercially pure aluminum, such as isused for cookware, becomes metallurgically annealed and loses asubstantial portion of its strength at such elevated temperatures. Theloss of tensile strength may lead to excessive deformation of the warein firing, or render it incapable of withstanding normal use.Accordingly, to compensate for this strength loss, the thickness of thealuminum must be increased to as much as 2.5 to 3.0 mm., resulting in anincreased usage of the relatively expensive material. In order toovercome the need for increasing the thickness, various organicdecorative coatings have been employed, such as thermalized nylon,polyamides, etc. These can be cured at a lower temperature of around600F. However, the saving realized by the elimination of the need forthe extra metalis largely offset by the added cost differential betweenorganic coating materials and inexpensive enamels.

Another approach to eliminate the need for using extra metal has been touse aluminum alloys which, though they anneal at the firing temperaturesof porcelain enamels, subsequently harden after a period of time withage and exposure. Unfortunately, these alloys generally containmagnesium which is not compatible with porcelain enamels. Therefore, thealloys must be coated with a substance, such as commercially purealuminum, in order to render the surface of the container compatiblewith the procelain coating. This type of construction requires the useof aluminum alloys which are also relatively expensive.

Certain problems have also been encountered with aluminum where it isdesired to support and anchor a non-stick'interior coating surface, suchas Teflon. Such non-stick surfaces must be bonded to the base metalsurface by way of physical rather than chemical bonds. Morespecifically, the bonding of non-stick coatings relies principally uponthe flow of the coating. material into pores and crests present upon thesurface of the base metal. Consequently, it has been found desirable toincrease the surface area of the base metal which is presented to thenon-stick coating-The most widely used method of increasing the surfacearea has been by blasting so as to score the surface to form a pluralityof peaks and pores which act as anchors for the non-stick coating. f

However, such scoring alone results in an inferior bonding between themetal and non-stick coating since thefiring temperatures of the coatingsoften the anchor peaks to the extent that the non-stick coating willnot bond well with the scored surface. This problem is accentuated whereit is desired to bond the non-stick coatingto a blank prior to formingthe blank into its final container shape.

In order to improve the quality of the bondbetween then'on-stick-coating and the aluminum ware, several approaches have beentried. One approach is to flame spray aluminum oxide particles,stainless steel particles or the like, on the aluminum to provide, ineffect, a secondary anchor base for the'non-stick coating which will notsoften during firing. This approach has been generally unsatisfactory,however, particularly where mass production methods are to be employedbecause of high cost and the difficulty of controlling the grain size ofthe particles and thedensity of the hard base matrix. Another approachhas been to fire bond a glass containing ceramic composition to theinterior of the aluminum ware. This bonding method provides good resultsif coated on relatively pure aluminum, but it can not be used with theage hardening aluminummagnesium alloys, since the ceramic composition isincompatible, as is porcelain, with such alloys.

Also where a non-stick coating is to be applied, it is important thatlocal hot spots in the heated surfacebe eliminated. Such hot spots tendto occur in the same areas which are directly impinged by the cookingflame or which rest directly upon the cooking coils of the range. It isimportant to minimize these hot spots since the present non-stickcoatings become unstable and are subject to deterioration when exposedto temperatures over about 500F. for extended time periods,

The cookware containers of my invention overcome the aforementioneddifficulties, and satisfy substantially all the criteria for an idealcontainer listed previously. In particular. the containers of myinvention have adequate strength to withstand normal use and willnotlose this strength if subjected to the elevated temperaturesnecessary to fire the exterior decorative pleasing aesthetic appearance.Finally, the container can satisfy all of the above criteria whilehaving a lower cost than is possible with an aluminum or aluminum alloycontainer which satisfies only some of the same criteria. I

BRIEF DESCRIPTION OF THE DRAWING In the course of this detaileddescriptiomthe drawing will frequently be referred to in which:

FIG. 1 is a perspective view of a cookware container in which theprinciples of my invention maybe incorporated; and

FIG. 2 is an enlarged cross-sectioned elevation view of the containertaken along line 2 2 of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, acooking container is shown having a substantially flat bottom wall 10,which is adapted to rest upon the burners or coils of a conventional gasor electric range (not shown)'and an upstanding, generally circularsidewall 11 extending upward from the bottom wall. to form a containerfor holding avolume of the foods, solids and/or liquids, which are to beheated. A conventional handle 12 may be attached to the sidewall 11 ofthe container to facilitate handling. I Referring to FIG. 2, theconstruction of the bottom and sidewalls of the container is shown indetail. FIG. 2 is not intended to be to scale and is not drawn to scale,the overall thickness of the container walls as I well as each of theplies or layers having been enlarged coatings or interior coatings orboth. The container surfaces are non-toxic and rust free 'even in theabsence of to show the details of my invention more clearly.

Each of the walls of the container comprises a mild or carbon steelcorelayer or ply 14. This core ply 14 is laminated between a pair ofnon-ferrous plies l6 and 18. Ply 16 is preferably aluminum so as toprovide for the later bonding of a non-stick coatingon the interior ofthe container. Ply 18 is also preferably aluminum,

but may also be formed of other materials, such as stainless steel,particularly where no further exterior decorative coating is to beapplied. Where plies 16 or 18 are of aluminum, the individual thicknessof these plies may be of the order of A (8 mm. The term nonferrous asemployed herein is not intended to limit plies 16 and 18 only tomaterials which contain no iron, but may include various iron alloyswhich do not display the usual iron characteristics, e.g. rust,magnetism, etc., such as the stainless steel previously mentioned.

The exterior of the upstanding sidewall 11 may be coated with'adecorative finish 20, which is preferably a porcelain or other'ceramicmaterial. Where an external decorative finish of porcelain is to beapplied, ply I8 is preferably a commercially pure aluminum whichexhibits suitable bonding properties with porcelain. Although porcelainis preferred as'a decorative finish, various other decorative finishesmay be employed,

such as polyamides and other organic compositions as set forth earlier.

A non-stick finish may also be applied to the interior of the container.Any one of a number of non-stick finishes may be used, such as variousmembers of the P.T.F.E. family, silicon base resins and the like. Priorto coating the interior of the container with the nonstick finish, ply16 is made receptive, physically or chemically, to an anchor frit ply 22which is coated upon and then heat bonded to ply 16 in order to providea strong anchor base to which the non-stick coating 24 may be firmlybonded. The frit ply 22 is preferably somewhat discontinuous and ispreferably one of the frits which are heat bonded to the interiorsurface of ply 16, such as the glass containing ceramic compositionmentioned earlier. A suitable composition is CN50Q available from TheFerro Corporation, Cleveland, Ohio. The interior non-stick coating 24 isthen applied to and firmly bonded to the discontinuous anchor ply aswell as to the metal.

The upper edge of the container may be rolled over or covered with acorrosion resistant decorative channeled rim 26.

To form the laminated multiply container of my invention, the mild orcarbon steel base core ply 14 is first coated on one or both sides witha thin layer or ply of the non-ferrous metal, such as aluminum. Any oneof a number of well-known coating processes, such as spraying, dipping,cladding and the like may be employed. Where the exterior ply 18 is tobe stainless steel. the stainless steel is deposited upon one side ofthe base core ply l4 and aluminum upon the other to form the interiorply 16. 1f the exterior is to be coated with a decorative coating 20,both plies 16 and 18 are preferably aluminum.

The anchor ply 22 is then coated upon ply 16 and the material is firedfor the purpose of bonding the anchor ply to the aluminum ply 16. if theporcelain decorative coating 20 is to be employed, it may be coated onthe external aluminum ply 18 prior to. firing and both the frit ply 22and the decorative coating may be fired together, since the bondingtemperature of both is approximately the same, about lO50F. Theaforementioned interior coating steps may be performed either upon theblank form which the final container is to be later formed or upon apreformed container.

If a solid aluminum container, as employed is the past, was subjected tothese heat bonding temperatures, the metal core of the container wouldhave to be increased in thickness in order to compensate for the loststrength due to annealing of the aluminum at the elevated heat bondingtemperatures of the coating, these temperatures being on the order of750F. lOF., whereas the melting point of aluminum is only about l220F.However, in the laminated container of my invention, the aluminum plies16 and 18 act primarily as bonding, heat conducting, and rust preventinglayers and the container strength is provided by the relativelyinexpensive steel base core ply 14, the strength of which issubstantially unchanged at the abovementioned temperatures. Thus, in thelaminated container of my invention softening of the aluminum plies 16and 18 is not an important consideration.

Once the frit anchor ply 22 has been heat bonded to ply 16, thenon-stick coating 24 may be applied by any one of a number of well-knownmethods.

adapted to optimize both the conductive and insulative qualities of thecontainer while actually furtherimproving the strength of the container.As set forth earlier, it is highly beneficial if the bottom wall 10 ofthe container is highly conductive in order to maximize heat transferfrom the heat source to the food in the container and to reduce thepossibility of hot spots which might occur in the container bottom withattendant possible damage to the coating and uneven heating of the food.It is also highly beneficial, if the sidewall 11 of the container, whichis ordinarily not exposed to the heat source, is at least somewhatinsulative in nature so as to minimize heat loss from the food throughthe walls of the container.

This may be readily accomplished in the laminated cookware of myinvention by varying the thickness of any one or all of the plies 14, 16and 18 between the sidewall 11 and bottom wall 10 of the container. Forexample, as shown in FIG. 2, the thickness of the steel core ply 14 maybe increased so as to be greater in the upstanding sidewall 11 of thecontainer than it is in the bottom wall 10. Conversely, the thickness ofone or both of the aluminum plies 16 and 18 may be increased so as to begreater in the bottom wall 10 than in the sidewall 11. Accordingly,since steel has a relatively low thermal conductivity and 1 aluminum arelatively high conductivity, heat transfer through the bottom of thecontainer to the food is unimpeded and the probability of hot spots isreduced due to lateral conduction in plies 16 and 18 of the bottom wall10. Heat transfer from the food through the sidewall 11 of the containeris reduced because of the greater thickness of poorly conducting steelin this region. Moreover, by increasing the thickness of the core ply 14in the sidewall 11, the strength of the sidewall of the container, whichis exposed to the maximum lateral stresses, is further increased. Inaddition to the added insulative qualities realized by the increase inthickness of the steel core ply l4 and the decrease in thickness of thealuminum plies l6 and 18 in the sidewall, further insulation on thesidewalls is realized by way of the decorative ceramic coating 20, whichitself acts as an insulator.

It should be understood that the embodiments of the invention which havebeen described are merely illustrative of some of the applications ofthe principles of the invention. Numerous modifications may be made bythose skilled in the art without departing from the true spirit andscope of the invention.

What is claimed is:

1. A laminated multiply cookware container comprising:

1 a cookware container which is adapted to be heated and having a bottomwall and a side wall, at least one of said walls including a first plycomprising a ferrous metal,

continuous second and third metal plies, one of said second and thirdplies comprising aluminum and the other of said plies selected from thegroup consisting of aluminum and stainless steel, wherein the entireexterior part of said one of said plies is free of ferrous content, andwherein the metal of at least one of said second and third plies has athermal conductivity greater than said ferrous metal and said first plybeing sandwiched between said second and third plies, and

a heat bonded inorganic coating ply bonded to said exterior part ofsaid. aluminum ply and on a face thereof remote from said first ply,said inorganic coating ply having a bonding temperature in excess of750F.

2. The container of claim 1 wherein said first ply comprises carbonsteel.

3. The container of claim 1 wherein'both of said second and third pliescomprise aluminum.

4. The container of claim 1 wherein the one of said second and thirdplies nearest the exterior of said container comprises stainless steeland the other comprises aluminum.

5. The container of claim 1 wherein said heat bonded coating comprisesan inorganic composition bonded to the one of said second and thirdplies nearest the exterior of said container. 7

6. The container of claim wherein said inorganic composition isporcelain.

7.-The container of claim 1 wherein said heat bonded coating plycomprises a frit on the one of said second and third plies nearest theinterior of said container, and a non-stick ply coating the interior ofsaid container and bonded to said frit coating. 1

8. The container ofclaim 1 wherein said metal of said second and thirdplies has a thermal conductivity substantially greater than said firstply, and the thickness of at least one of said second and third plies isgreater in the area of said container which is to be exposed to the heatsource than in the area of said container which is not exposed to theheat source.

9. The container of claim 8 wherein the thickness of said first ply issmaller in said first mentioned area than in said second mentioned area.

10. The container of claim 1 wherein the thickness of at least one ofsaid plies varies in different areas of the container.

11. The container of claim 1 wherein the minimum thickness of saidsecond and third plies is about A mm.

12. A laminated multiply cookware container com- 8 prising incombination:

a first carbon steel ply, second and third aluminum plies with at leastthe entire exterior portion of each of such plies being free of ferrouscontent said first carbon steel ply being sandwiched between saidaluminum plies, an inorganic heat bonded coating bonded to said exposedsurface of the one of said aluminum plies nearest the exterior of saidcontainer, an inorganic anchor coating bonded to said exposed surface ofthe other of said aluminum plies nearest the interior of-said container,a non-stick coating bonded to said anchor coating. 13. The container ofclaim 12 wherein the thickness of at least one of said aluminum plies isgreater in the area of the container which is to be exposed to the heatsource than in the area which is not exposed to the heat source and thethickness of the carbon steel ply is smaller in the first mentioned areathan the last menply having a thermal conductivity which is substan-'tially greater than said given conductivity of said first ply, I

the thickness of said second ply being greater in a first wall area ofsaid container which is to be exposed to the heat source than in asecond wall area of the container which is not exposed to the heatsource, and the thickness of said first ply being greater in said secondarea than said first area, whereby the conductivity through said firstwall area is substantially greater than through said second wall area.

16. The container of claim 15 wherein said first ply is a ferrous metaland said second ply is a non-ferrous metal.

17. The container of claim 16 wherein said second ply is aluminum.

1. A laminated multiply cookware container comprising: a cookwarecontainer which is adapted to be heated and having a bottom wall and aside wall, at least one of said walls including a first ply comprising aferrous metal, continuous second and third metal plies, one of saidsecond and third plies comprising aluminum and the other of said pliesselected from the group consisting of aluminum and stainless steel,wherein the entire exterior part of said one of said plies is free offerrous content, and wherein the metal of at least one of said secondand third plies has a thermal conductivity greater than said ferrousmetal and said first ply being sandwiched between said second and thirdplies, and a heat bonded inorganic coating ply bonded to said exteriorpart of said aluminum ply and on a face thereof remote from said firstply, said inorganic coating ply having a bonding temperature in excessof 750*F.
 2. The container of claim 1 wherein said first ply comprisescarbon steel.
 3. The container of claim 1 wherein both of said secondand third plies comprise aluminum.
 4. The container of claim 1 whereinthe one of said second and third plies nearest the exterior of saidcontainer comprises stainless steel and the other comprises aluminum. 5.The container of claim 1 wherein said heat bonded coating comprises aninorganic composition bonded to the one of said second and third pliesnearest the exterior of said container.
 6. The container of claim 5wherein said inorganic composition is porcelain.
 7. The container ofclaim 1 wherein said heat bonded coating ply comprises a frit on the oneof said second and third plies nearest the interior of said container,and a non-stick ply coating the interior of said container and bonded tosaid frit coating.
 8. The container of claim 1 wherein said metal ofsaid second and third plies has a thermal conductivity substantiallygreater than said first ply, and the thickness of at least one of saidsecond and third plies is greater in the area of said container which isto be exposed to the heat source than in the area of said containerwhich is not exposed to the heat sourCe.
 9. The container of claim 8wherein the thickness of said first ply is smaller in said firstmentioned area than in said second mentioned area.
 10. The container ofclaim 1 wherein the thickness of at least one of said plies varies indifferent areas of the container.
 11. The container of claim 1 whereinthe minimum thickness of said second and third plies is about 1/4 mm.12. A laminated multiply cookware container comprising in combination: afirst carbon steel ply, second and third aluminum plies with at leastthe entire exterior portion of each of such plies being free of ferrouscontent said first carbon steel ply being sandwiched between saidaluminum plies, an inorganic heat bonded coating bonded to said exposedsurface of the one of said aluminum plies nearest the exterior of saidcontainer, an inorganic anchor coating bonded to said exposed surface ofthe other of said aluminum plies nearest the interior of said container,a non-stick coating bonded to said anchor coating.
 13. The container ofclaim 12 wherein the thickness of at least one of said aluminum plies isgreater in the area of the container which is to be exposed to the heatsource than in the area which is not exposed to the heat source and thethickness of the carbon steel ply is smaller in the first mentioned areathan the last mentioned area.
 14. The container of claim 12 wherein theminimum thickness of said second and third aluminum plies is about 1/4mm.
 15. A laminated multiply cookware container comprising: a first plyhaving a given thermal conductivity, a second ply laminated to saidfirst ply, said second ply having a thermal conductivity which issubstantially greater than said given conductivity of said first ply,the thickness of said second ply being greater in a first wall area ofsaid container which is to be exposed to the heat source than in asecond wall area of the container which is not exposed to the heatsource, and the thickness of said first ply being greater in said secondarea than said first area, whereby the conductivity through said firstwall area is substantially greater than through said second wall area.16. The container of claim 15 wherein said first ply is a ferrous metaland said second ply is a non-ferrous metal.
 17. The container of claim16 wherein said second ply is aluminum.